Device for a Borehole Arrangement

ABSTRACT

A device for a borehole arrangement, in which a casing for a borehole is formed of at least one casing section, and in which there is placed at a downhole end portion of the casing at least one downhole tool, for example a drilling tool, wherein the casing is provided with two or more pipe bores, each separately extending continuously through a substantial part of the length of the casing and being separated in a fluid-tight manner from adjacent pipe bores and from an external annulus defined by the external mantle surface of the pipe and a borehole wall.

The invention relates to a multibore casing for a borehole, in particular for an exploration or production well for hydrocarbons of the type of well that exhibits a long horizontal extent, and in particular a well which is formed by there being placed in the open well bore an automotive downhole tractor provided with means for drilling.

From the state of the art is known the use of casing with a stepped diameter and the conveyance of fluids (drilling fluid etc.) in a pipe string, for example a drill string or coiled tubing, in the centre bore of the casing and return of the fluids in an annulus between the casing and the pipe string placed internally in the casing, the drilling tool being moved forward by the pipe string being moved down and outwards. When new sections of casing are being placed into the open borehole, the drill string must first be pulled up. When the extent of the borehole is several kilometres, it stands to reason that each tripping out and tripping in of the drill string is both time-consuming and costly. A long borehole will also exhibit a very small diameter at its outer end due to the constantly stepped diameter of the casing sections. This limits the possibility of using complex downhole tools in a completion string.

When the borehole diameter decreases, the size of the annulus between the casing and drill string will also decrease. This affects the flow rate of, for example, the drilling fluid which is carrying cuttings to the surface, as the specific annulus volume increases from the lower/outer end of the borehole towards the earth surface/seabed. Thereby the flow rate decreases, and this may lead to the sedimentation of cuttings with the risk of the annulus passage clogging up.

From Eventure Global Technology, among others, it is known to use a borehole with the same diameter throughout, the borehole being cased, as the drilling proceeds, with expandable casings in the lower end portion of the borehole. The drawbacks of this technique are high costs and also uncertainty about the mechanical strength and sealing against leakage, in the pipe connections among other things.

The invention has as its object to remedy or reduce at least one of the drawbacks of the prior art.

The object is achieved through features specified in the description below and in the claims that follow.

The invention relates to a technique for drilling and constructing production wells for hydrocarbons, in particular long, horizontal wells. In a first aspect of the invention there are used double-walled casings with several passages in the annulus between the two pipe walls. The passages are arranged for conveying fluids and/or extending cables for the transfer of signals or power, for example. The casing preferably exhibits the same diameter throughout the length of the well.

Alternatively, the casings may include channels placed on the external side of the pipes or integrated into the pipe wall.

The casing may advantageously include one or more channels on the outside of the pipe for shielding cables for the conveyance of electrical power or control and/or monitoring signals between a surface installation and downhole installations along the casing or at the end portion of the casing.

Another aspect of the invention relates to remote-controlled packers that are placed on the periphery of the casing, preferably one for each pipe section, the packer being arranged to be releasably set in a fluid-sealing manner against the wall of the borehole. The packer includes means for controlled fluid flow at least in the direction from the downhole end portion of the casing. In this aspect is achieved that a fluid, for example drilling mud, of a specific weight etc. adjusted to the properties of the adjacent formation, may be kept enclosed in the part of the annulus outside the casing defined between two packers. When the casing is moved down the borehole and drilling mud is supplied to said annulus at the downhole end portion of the casing, said enclosed fluid is pushed through the open fluid passage of its respective packer above into the section of the annulus above. Thereby the adjusted fluid maintains its position relative to the surrounding formation while the casing is moved down. When the moving of the casing has been stopped, the packers are set again against the borehole wall and the means in the packers for fluid flow are possibly closed by remote control. Thereby the risk of a formation being affected by a fluid with properties having an adverse effect on the formation is reduced.

Advantageously, the packers may include sensors for monitoring the borehole, formation and/or casing.

Another aspect of the invention relates to a remote-controlled downhole tool, for example a downhole tractor, which is placed in the open, uncased well bore adjacent to and in front of (below) the downhole end portion of the casing, the downhole tool being provided at least with means which are arranged to drill in the well formation. This enables well drilling while the casing is moved forward behind the downhole tool by means of gravity and possibly by the downhole tool being mechanically connected to a downhole end portion of the casing, so that the casing can be pulled forward by means of the downhole tractor.

The downhole tool is in fluid-communicating and signal-communicating connection with a surface installation, for example a drilling rig, by fluid, electric power, control and monitoring signals being conveyed through the appropriate lines at the wall of the casing and also suitable flexible lines connecting the downhole end portion of the casing and the downhole tool.

One packer is placed at the downhole end of the casing, thereby defining the open well bore to include a portion extending only from the end of the borehole to the downhole end of the casing. Thereby only a short borehole portion is the subject of hole cleaning by flushing with drilling mud, for example.

The invention relates in particular to a device for a borehole arrangement, in which a casing for a borehole is formed of at least one casing section, and in which there is placed at the downhole end portion of the casing at least one downhole tool, for example a drilling tool, characterized in that the casing is provided with two or more pipe bores, each separately extending continuously through a substantial part of the length of the casing and being separated in a fluid-tight manner from adjacent pipe bores and from an external annulus defined by the external mantle surface of the pipe and the wall of the borehole.

At least one pipe bore is preferably arranged in the wall of the casing or on or at the external mantle surface of the casing.

Advantageously, the casing includes one or more channels extending in the axial direction on the external mantle surface of the casing and being arranged to receive one or more lines for fluid transport or for the transfer of control and/or monitoring signals between a surface installation and downhole installations placed along the casing or at the downhole end portion of the casing.

The casing is preferably provided with one or more annular packers surrounding the casing and being arranged to selectively and fluid-communicatingly define a portion of the external annulus by the packer being releasably set against the wall of the borehole.

Alternatively, a plurality of the packers are placed on the casing adjacent to the downhole end portion of the casing, the packers including means for selective release and fixing relative to the external mantle surface of the casing and selective fixing against the borehole wall.

Preferably, the packers are provided with one or more closable packer fluid passages.

The packer fluid passages are advantageously arranged to close to fluid passage in a chosen direction and, at the same time, to stay open to fluid passage in the opposite direction.

The packer fluid passages are advantageously formed as check valves.

Preferably, the packer is provided with means for controlled fixing and release of the packer relative to the borehole wall.

Preferably, an end cover is placed in a fluid-sealing manner on the downhole end portion of the casing.

Preferably, the end cover is provided with one or more closable end cover fluid passages.

Advantageously, the end cover is provided with one or more closable passages for downhole equipment.

Advantageously, the end cover fluid passages are arranged to close to fluid passage in a chosen direction and at the same time stay open to fluid passage in the opposite direction.

Alternatively, the fluid passages are formed as check valves.

Advantageously, the end cover is provided with one or more fluid-sealingly closable passages for downhole equipment.

In one aspect the downhole tool is a downhole tractor which is arranged to move in an open, uncased portion of the borehole at the downhole end portion of the casing and to carry means for working the borehole.

Preferably, the downhole tool is connected in a fluid-communicating manner to at least one of the pipe bores of the casing for the circulation of one or more fluids between a surface installation and the downhole tool with return to the surface installation, possibly between the surface installation, the downhole tool and the open borehole with return to the surface installation.

Advantageously, the downhole tool is mechanically connected to the downhole end portion of the casing and is arranged to pull the casing into the open portion of the borehole.

Advantageously, the downhole end portion of the casing is mechanically connected to a pulling device on the downhole tool.

The pulling device is preferably a winch.

In one aspect of the invention at least one of said two or more bores is preferably provided with selectively closable openings in said downhole end portion of the casing.

In what follows, is described a non-limiting example of a preferred embodiment which is visualized in the accompanying drawings, in which:

FIG. 1 shows a principle sketch of a cut-through hydrocarbon well with a derrick and casing, downhole tool and means for the circulation of a drilling fluid connected to the casing;

FIG. 1 a shows, on a larger scale, a longitudinal section Ia-Ia of FIG. 1 b through a downhole end portion of the casing with an end cover and a casing portion at an annulus packer;

FIG. 1 b shows a cross-section Ib-Ib of FIG. 1 a of a downhole end portion of the casing at the end cover;

FIG. 2 shows on the same scale as FIG. 1 a section of the installation with the casing in a position prepared for extension, the means for the circulation of the drilling fluid being disconnected;

FIG. 3 shows a section of the installation, in which the casing has been extended;

FIG. 4 shows a section of the installation, in which the casing has been pulled partially into the well bore; and

FIG. 5 shows a section of the installation, in which the means for the circulation of a drilling fluid have been reconnected and the casing has been pulled into the well bore.

Reference is made primarily to the FIGS. 1, 1 a and 1 b. A derrick 1 is located at a borehole 3 which extends through an underground structure 5 and up to an open, that is to say an uncased, downhole end portion 3 a, the borehole 3 forming a borehole wall 5 a. A substantial part of the borehole 3 is provided with a casing 11 including a centre bore 12 and a pipe wall 13. The pipe wall 13 is provided with several pipe bores 13 a, 13 b extending through it, each separated in a fluid-tight manner from the other pipe bores 12, 13 a, 13 b and from an annulus 14 formed between the casing 11 and the borehole wall 5 a.

The casing 11 is provided with several annular packers 15, 15 a surrounding the casing 11 and being arranged to bear sealingly on the borehole wall 5 a, one pair of adjacent packers 15, 15′ defining a portion of the annulus 14 relative to adjacent annulus portions formed by other packers 15, 15′.

The packer 15 is provided with means (not shown) for controlled fixing and release of the packer 15 relative to the borehole wall 5 a. The packer 15 is also provided with packer fluid passages 15 a (see FIG. 1 a) which are arranged to close to fluid passage in a chosen direction and at the same time stay open to fluid passage in the opposite direction. The direction of flow of fluid through the packer fluid passage 15 a is preferably from the downhole end portion 11 b of the casing 11 towards the derrick 1. The packer fluid passage 15 a is typically formed as a check valve which can be closed.

A downhole end portion 11 a of the casing 11 is provided with a fluid-sealing end cover 11 b. The end cover 11 b is provided with a fluid passage 11 c, 11 d corresponding to the pipe bores 13 a, 13 b. A first end cover fluid passage 11 c is provided with means for fluid communication between the pipe bore 13 a and a downhole tool 21 via a flexible line 22. A second end cover fluid passage 11 d is in fluid communication with the open end portion 3 a of the borehole 3 and with the pipe bore 13 b. The end cover fluid passages 11 c, 11 d are provided with means 11 e, 11 f which are arranged for selective opening and closing to fluid flow, for example by means of remote control.

The downhole tool 21 is typically a downhole tractor of a type known per se.

The end cover 11 b is also provided with a peripherally placed, annular end cover packer 11 g which is provided with means (not shown) for controlled fixing and release of the end cover packer 11 g relative to the borehole wall 5 a. In a manner corresponding to that of the packer 15, the end cover packer 11 g is provided with a packer fluid passage 15 a which is arranged to close to fluid passage in a chosen direction and at the same time stay open to fluid passage in the opposite direction. The direction of flow of fluid through the packer fluid passage 15 a is preferably from the downhole end portion 11 b of the casing 11 towards the derrick 1.

Externally, the casing 11 is also provided with a recessed channel 16 (se FIG. 1 b) extending in the entire axial length of the casing 11. The channel 16 is arranged for receiving and retaining cables 17, for example, for conveying measuring data, control signals etc. The packers 15 and end cover 11 b are provided with fluid-sealing cable passages complementary to the channel 16.

The downhole tool 21 has the form of a downhole tractor which is provided with propulsion means 23 a which are arranged to be selectively engaged with the borehole wall 5 a. Via the flexible line 22, the first end cover fluid passage 11 c of the end cover 11 b, the pipe bore 13 a of the casing 11 and a flexible pump hose 31 a, the downhole tool 21 is connected in a fluid-communicating manner to a pump 31 with associated fluid reservoir (not shown) placed at the surface installation. Via the cables 17 the downhole tool 21 is also connected to a control system 33 placed on or above the ground surface and arranged to store and interpret measuring data, generate control signals etc.

The downhole tool 21 is typically provided with means for working the borehole 3, for example a drill bit 24.

The downhole tool 21 is also provided with a winch 23. A wire 23 c of tensile strength is extended between the winch 23 and the end portion 11 a of the casing 11 and releasably attached thereto. By means of a drive powered by an available energy source and a remote control, the winch is arranged to wind or unwind the wire 23 c.

The downhole tool 21 is also arranged to receive fluid under pressure through the flexible line 22 for the movement of the propulsion means 23 a, operation of the winch 23 and drill bit 24. The downhole tool 21 includes fluid outlet openings (not shown) which are of such arrangement that out-flowing fluid may flush the open borehole end portion 3 a before the fluid flows through the second end cover fluid passage 11 d, through the second pipe bore 13 b and via a flexible tank line 32 a into a fluid collecting tank 32. The fluid is typically drilling mud which is arranged to maintain pressure control in the well, lubricate the downhole tool 21 and carry off cuttings from the borehole 3.

Arrows indicate the ordinary direction of flow of drilling mud during drilling.

FIGS. 2-5 show different stages in the extension of the casing 11 by a casing section 11 a being joined to the casing 11 at the upper end of the casing 11.

By the use of the device according to the invention a borehole is formed in the ordinary manner by, for example, a casing being driven down into loose masses located above the structure to be drilled, so that a cased hole is formed down to the bedrock 5. After that, an uncased borehole 3 is formed through the bedrock 5 as far as feasible without the borehole wall 5 a having to be secured with casing, appropriate drilling equipment being used, for example an ordinary drill string with a rotating drill bit and drilling mud conveyance through the drill string to the drill bit and return in the annulus between the drill string and the borehole wall.

When the drilling approaches a structure which requires casing of the borehole 3, the drilling equipment is removed. The downhole tool 21 is joined to a first casing section 11 a, which is provided with an end cover 11 b at its downhole end portion 11 a, by means of the flexible line 22 and the wire 23 c. By means of the cables 17 the downhole tractor 21 is connected to the control system 33 for the storing and interpretation of measured data, generation of control signals etc.

The downhole tool 21 and the first casing section 11 a are moved down into the borehole 3. The casing 11 is extended with new sections 11 a as required, the sections 11 a being joined together in a fluid-sealing manner, so that continuous pipe bores 13 a, 13 b and channel 16 extend over the entire length of the joined casing 11, and the cables 17 extend along the casing 11 as the cables 17 are laid and fixed within the channel 16.

When the downhole tool 21 has reached the bottom of the predrilled borehole 3 and the borehole 3 is cased, preparations are made for drilling and moving forward casing according to the invention. The packers 11 g, 15 are set against the borehole wall 5 a. Weight fluid with the prescribed properties is pumped through one or more pipe bores 12, 13 a, 13 b down to the uncased downhole end portion 3 a and up into the annulus 14 through the packer fluid passages 15 a.

The downhole tool 21 is set into operation as drilling fluid is pumped by means of the pump 31 through the pipe bore 13 a to the downhole tractor 21 and the propulsion means 23 a and drill bit 24, these being activated by means of the control system 33. As the open borehole portion 3 a is extended, it is flushed with the drilling mud flowing out of the fluid outlets (not shown) of the downhole tool 21. The drilling mud together with the cuttings from the drilling flows via the pipe bore 13 b back to the surface where it is collected in the fluid collecting tank 32, in which it undergoes treatment in a manner known per se. When the downhole tool 21 moves forward during the drilling, the wire 23 c is preferably pulled out by the winch 23, so that the downhole tractor does not exert pull on the casing 11.

When the open borehole portion 3 a has got a suitable length, the downhole tool is fixed against the borehole wall 5 a in a manner known per se by means of the propulsion means 23 a. The packers 11 g, 15 are released from the borehole wall 5 a, weight fluid is pumped down the open borehole portion 3 a and the winch 23 is started. The casing 11 is thereby pulled into the borehole 3 as weight fluid is flowing through the packer fluid passages 15 a into the annulus 14. The packer fluid passages 15 a being arranged for fluid flow only in the direction away from the open downhole borehole portion 3 a, the weight fluid will, to a substantial degree, maintain its initial position relative to the surrounding rock structure 5. Thereby, movement of the casing 11 according to the invention will maintain a prescribed placement of weight fluid with properties adjusted to the surrounding structures, the prevailing pressure conditions etc. When the casing 11 has been pulled forward into the desired position, either by having reached a desired distance from the downhole tractor 21, or by a new casing section 11 a having to be joined to the upper end of the casing 11, the packers 11 g, 15 are set again against the borehole wall 5 a.

When a new casing section 11 a is to be joined to the casing 11, the hoses 31 a, 32 a are disconnected, a fluid-tight joining is carried out and the join of the casing 11 is tested in the prescribed manner. After the hoses 31 a, 32 a have been reconnected, the drilling operation and forward movement of the casing 11 are then repeated, as it is described above, until the desired length of the borehole 3 has been reached and the borehole has been cased.

The end cover 11 b may advantageously be provided with a passage (not shown) for bottom-hole tools, the passage being fluid-sealingly closable by means of, for example, remote control from the control system 33. Thereby, after release from the end cover 11, the downhole tractor 21 can be retrieved from the borehole in a manner known per se, and another bottom-hole tool may be moved into the open end portion 3 a of the borehole 3.

In an alternative embodiment all or a plurality of the packers 15 may be placed on the casing 11 adjacent to the downhole end portion 11 a of the casing 11 when the insertion of the casing 15 into the borehole 3 starts. The packers 15 are provided with means (not shown) enabling selective release and fixing of the packers 15 relative to the external mantle surface of the casing 11 and selective fixing of the packer 15 to the borehole wall 5 a during the moving forward of the casing within the borehole 3. Thereby the packers 15 may be set where there is a need for them according to analyses of the borehole 3. 

1. A device for a borehole arrangement, in which a casing for a borehole is formed of at least one casing section, and in which there is placed at a downhole end portion of the casing at least one downhole tool, for example a drilling tool, wherein the casing is provided with two or more pipe bores, each separately extending continuously over a substantial part of the length of the casing and being separated in a fluid-tight manner from adjacent pipe bores and from an external annulus defined by the external mantle surface of the pipe and a borehole wall.
 2. The device in accordance with claim 1, wherein at least one pipe bore is arranged in the wall of the casing.
 3. The device in accordance with claim 1, wherein at least one pipe bore is arranged on or at the external mantle surface of the casing.
 4. The device in accordance with claim 1, wherein the casing includes one or more channels extending in the axial direction in the external mantle surface of the casing and being arranged to receive one or more lines for fluid conveyance or for the transfer of control and/or monitoring signals between a surface installation and downhole installations disposed along the casing or at the downhole end portion of the casing.
 5. The device in accordance with claim 1, wherein the casing is provided with one or more annular packers surrounding the casing and being arranged to define selectively and fluid-communicatingly a portion of the external annulus, the packer being releasably set against the wall of the borehole.
 6. The device in accordance with claim 5, wherein a plurality of the packers are placed on the casing adjacent to the downhole end portion of the casing, the packers including means for the selective release and fixing relative to the external mantle surface of the casing and selective fixing against the borehole wall at a random point in the axial extent of the casing.
 7. The device in accordance with claim 5, wherein the packers are provided with one or more closable packer fluid passages.
 8. The device in accordance with claim 7, wherein the packer fluid passages are arranged to close to fluid passage in a chosen direction and at the same time stay open to fluid passage in the opposite direction.
 9. The device in accordance with claim 7, wherein the packer fluid passages are formed as check valves.
 10. The device in accordance with claim 5, wherein the packer is provided with means for the controlled fixing and release of the packer relative to the borehole wall.
 11. The device in accordance with claim 1, wherein an end cover is placed fluid-sealingly on the downhole end portion of the casing.
 12. The device in accordance with claim 11, wherein the end cover is provided with one or more closable end cover fluid passages.
 13. The device in accordance with claim 12, wherein the end cover fluid passages are arranged to close to fluid passage in a chosen direction and at the same time stay open to fluid passage in the opposite direction.
 14. The device in accordance with claim 12, wherein the end cover fluid passages are formed as check valves.
 15. The device in accordance with claim 11, wherein the end cover is provided with one or more fluid-sealingly closable passages for downhole tools.
 16. The device in accordance with claim 1, wherein the downhole tool is a downhole tractor which is arranged to move in an open, uncased portion of the borehole at the downhole end portion of the casing and to carry means for working the borehole.
 17. The device in accordance with claim 16, wherein the downhole tool is connected in a fluid-communicating manner to at least one of the pipe bores of the casing for the circulation of one or more fluids between a surface installation and the downhole tool with return to the surface installation, possibly between the surface installation, the downhole tool and the open borehole with return to the surface installation.
 18. The device in accordance with claim 16, wherein the downhole tool is mechanically connected to the downhole end portion of the casing and is arranged to pull the casing into the open portion of the borehole.
 19. The device in accordance with claim 18, wherein the downhole end portion of the casing is mechanically connected to a pulling device on the downhole tool.
 20. The device in accordance with claim 19, wherein the pulling device is a winch.
 21. The device in accordance with claim 1, wherein at least one of said two or more pipe bores is provided with selectively closable openings in said downhole end portion of the casing. 